I have been getting "OSError: [Errno 13] Permission denied" for quite a while now. If I keep trying to do the action where I get the error (book rename, author rename, book format conversion, etc.) it eventually works. I see many posts about this error and none seem to be relevant to my situation and are a few years old.

I am using Calibre 1.34.0 on Windows 74 64-bit. My library is on a NAS device formatted as EXT 4. I do have multiple computers that hit the library, but never at the same time. There is no A/V SW scanning the NAS share where the library is located.

I guess I need to try moving the library to one of the computers harddrives and see if the issue goes away. The library has been on the NAS share for years with no problem. The issue seemed to start after one of the updates I did a few months back. I was hoping one of the updates along the way would make it go away.

Bottom line is that Calibre is not intended to work with the library on a server or NAS. The fact that you were able to do so was fortuitous, the fact that it doesn't work now means good fortune has deserted you. I imagine that support for libraries located on servers and NAS devices will probably coincide with the release of multi-user calibre.

There are a number of threads in the forum that discuss this, for some people NFS seems to work whereas CIFS and SMB don't.